1. Field of the Invention
The present invention relates to a position measurement and control apparatus and method. More particularly, the present invention relates to an apparatus and method for controlling the position of an object with high precision.
2. Description of the Related Art
FIG. 1 is a block diagram illustrating a conventional incremental encoder sensing system for position measurement. Referring to FIG. 1, the conventional incremental encoder sensing system includes an analog encoder sensor 100, an analog inverter 110, a quadrature signal generator 120, a 4:1 analog multiplexer 130, an analog-to-digital (A/D) converter 140, and an absolute position converter 150.
The analog encoder sensor 100 outputs pseudo sine or cosine waves X and Y. The pseudo sine or cosine waves X and Y have a phase difference of 90 degrees. Thereafter, the pseudo sine or cosine waves X and Y are inverted by the analog inverter 110, and the inverted pseudo sine or cosine waves nX and nY are input to the 4:1 analog multiplexer 130 together with the pseudo sine or cosine waves X and Y.
The quadrature signal generator 120 receives the pseudo sine or cosine waves X and Y and enables the 4:1 analog multiplexer 130 to select and output one of the four waves input thereto. A wave or signal output from the 4:1 analog multiplexer 130 provides rather general position information to the A/D converter 140, and the A/D converter 140 processes the position information received from the 4:1 analog multiplexer 130, thereby obtaining more specific position information. The absolute position converter 150 further refines the position information received from the A/D converter 140, thereby providing even more specific position information. The position information output from the absolute position converter 150 is used in, for example, a servo system.
The conventional incremental encoder sensing system divides one cycle of a pseudo sine wave by 4 by using a comparator, thereby obtaining general position information. Thereafter, an analog signal containing specific position information is selected using the 4:1 analog multiplexer 130 and then digitalized using the analog-to-digital converter 140. Accordingly, position information in one cycle of the pseudo sine wave can be obtained using the general position information and the specific position information.
Examples of conventional incremental encoder sensing systems are disclosed in U.S. Pat. Nos. 4,457,639 and 5,933,106.
The pseudo sine or cosine waves X and Y output from the analog encoder 100 of FIG. 1 are input to an analog multiplier, thereby obtaining signals with two times higher frequencies than those of the pseudo sine or cosine waves X and Y. The signals are used as information for position determination. This type of technique is disclosed in Korean Patent Application No. 2003-0048648. However, the analog multiplier is large and expensive, and thus it is difficult to apply the analog multiplier to a device with a high integration density.
In order to increase the precision of position determination of the conventional incremental encoder sensing system of FIG. 1, the structure of the conventional incremental encoder may inevitably become very complicated and may need a processor, such as a central processing unit (CPU), in which case the structure of the conventional incremental encoder sensing system becomes even more complex. When assisted by the processor, the conventional incremental encoder sensing system needs a predetermined software program to control the processor, in which case the performance of the conventional incremental encoder sensing system inevitably deteriorates.
In short, in order to enhance the precision of position determination of the conventional incremental encoder sensing system, the structure of the corresponding incremental encoder sensing system may need to become excessively complicated, which results in deterioration of the performance of the corresponding incremental encoder sensing system. Therefore, it is difficult to achieve a desired level of precision for position determination by using the conventional incremental encoder sensing system.
Accordingly, there is a need for an incremental encoder system having enhanced precision while not being overly complex or expensive.